This invention relates to a new composition of matter comprising crystalline aluminosilicate zeolites, and particularly to zeolites that have been ion exchanged so as to exchange the cations therein for other cations. More particularly, the invention relates to crystalline aluminosilicate zeolites having exchanged thereinto molybdenum-containing cations.
Crystalline aluminosilicate zeolites are well-known porous materials for drying gases, catalyzing hydrocarbon conversion reactions, and absorbing certain compounds in preference to others. Such zeolitic materials have an ordered crystalline structure and consist essentially of a crystal framework of AlO.sub.4 and SiO.sub.4 tetrahedra crosslinked by shared oxygen atoms. The electrovalence of the crystal framework is negative and is balanced by the presence of cations, usually metal cations or hydrogen cations. The empirical chemical formula for crystalline aluminosilicate zeolites may be expressed in terms of molar ratios of oxides as follows: EQU M.sub.2/n O:Al.sub.2 O.sub.3 :xSiO.sub.2 :yH.sub.2 O
where Al.sub.2 O.sub.3 and SiO.sub.2 represent the AlO.sub.4 and SiO.sub.4 constituents making up the electronegative crystalline framework, H.sub.2 O is the water of hydration, x and y are the number of moles of SiO.sub.2 and H.sub.2 O, respectively, per mole of Al.sub.2 O.sub.3 in the crystal framework, and M.sub.2/n O represents the components required to balance the negative charge of the crystalline aluminosilicate framework per mole of Al.sub.2 O.sub.3 in the framework, with n being the cation valence of M.
Some crystalline aluminosilicate zeolites occur naturally. Chief among these are analcime, brewsterite, chabazite, clinoptilolite, erionite, faujasite, ferrierite, gismondine, gmelinite, mesolite, mordenite, natrolite, offretite, phillipsite, paulingite, scolecite, stilbite, and thomsonite. Many of the foregoing naturally-occurring zeolites may also be prepared synthetically. In addition, numerous synthetic zeolites are known, chief among which are the following listed with U.S. Patents that disclose methods for synthetically preparing such zeolites, said U.S. Patents being incorporated by reference herein: Zeolite A (U.S. Pat. No. 2,882,243), Zeolite B (U.S. Pat. No. 3,008,803), Zeolite F (U.S. Pat. No. 2,996,358), Zeolite H (U.S. Pat. No. 3,010,789), Zeolite L (U.S. Pat. No. 3,216,789), Zeolite T (U.S. Pat. No. 2,950,952), Zeolite W (U.S. Pat. No. 3,012,853), Zeolite X (U.S. Pat. No. 2,882,244), and Zeolite Y (U.S. Pat. No. 3,130,007). Many other synthetic zeolites may be prepared by methods known in the art, including, for example, Zeolite Omega, Zeolite ZSM-5, Zeolite ZSM-4, Zeolite P, Zeolite N, Zeolite D, Zeolite O, Zeolite S, and Zeolite Z.
One advantageous feature of virtually all crystalline aluminosilicate zeolites is that they are ion-exchangeable, that is, the cations in the zeolite that balance the electronegative charge of the crystalline framework are replaceable with other cations. Crystalline aluminosilicates, whether naturally-occurring or synthetically prepared, are usually in the sodium form, and it is often necessary to remove the sodium and replace it with other cations. For example, the sodium form of Zeolite Y proves inactive when used as a catalyst for cracking hydrocarbons, and as a result, it is desirable to replace the sodium with rare earth cations or hydrogen ions, or both, in order to stabilize the zeolite for catalytic cracking purposes. This may easily be accomplished by methods well-known in the art, and methods are known for ion-exchanging any of a number of metal-containing cations into a crystalline aluminosilicate. U.S. Pat. No. 3,013,982 discloses the ion exchange of nickel, silver, mercury, cadmium, lead, copper, iron, and thallium into crystalline aluminosilicates, U.S. Pat. No. 3,140,253 discloses rare earth-exchanged zeolites, U.S. Pat. No. 3,200,082 discloses copper, silver, gold, chromium, zinc, cadmium, lead, tin, cobalt, ruthenium, iron, nickel, rhodium, palladium, osmium, iridium, and platinum exchanged zeolites, U.S. Pat. No. 3,954,671 discloses manganese and alkaline earth metal exchanged zeolites, U.S. Pat. No. 3,969,276 discloses lithium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium, copper, and silver-exchanged zeolites, and U.S. Pat. No. 4,083,807 discloses antimony, bismuth, and manganese exchanged zeolites. In addition, it is also well-known that ammonium ions and hydrogen ions can be ion exchanged into a crystalline aluminosilicate zeolite (e.g., by the method taught in U.S. Pat. No. 3,130,006).
As should be apparent from the foregoing, virtually every common metal or semi-metal listed in the Periodic Table has been ion-exchanged into a crystalline aluminosilicate zeolite. One notable exception, however, is molybdenum. Despite many efforts to introduce molybdenum into crystalline aluminosilicate zeolites by ion exchange, there is still no successful method to ion exchange substantial amounts of molybdenum into aluminosilicate zeolites. The primary problem is that molybdenum is stable in aqueous media in the form of anionic species, such as MoO.sub.4.sup.-2 or Mo.sub.7 O.sub.24.sup.-6, and since the zeolite can only exchange cations, the impossibility of introducing such anionic species into an aluminosilicate by ion exchange is self-evident. Attempts to use cation forms of molybdenum have also proven unsuccessful, largely due to instability problems with molybdenum-containing cations and/or the difficulty in overcoming unfavorable ion exchange equilibria.
The main object of the invention, therefore, is to provide a crystalline aluminosilicate zeolite containing molybdenum in an ion-exchangeable form. A further object is to provide a method for ion exchanging molybdenum-containing cations into crystalline aluminosilicate zeolites. It is a further object to provide a composition of matter comprising a crystalline aluminosilicate zeolite having at least some of its ion exchange capacity satisfied with cations containing molybdenum. A specific object is to provide a molybdenum-exchanged Zeolite Y and a method for preparing such a Zeolite Y. It is yet another object of the invention to utilize molybdenum-exchanged crystalline aluminosilicate zeolites in oxide or sulfided forms as catalysts for dealkylating toluene and/or alkylated naphthenes, for cracking hydrocarbons, and for hydrocracking hydrocarbons. These and other objects and advantages will become clear to those skilled in the relevant art from the following description of the invention.